Shutting Down Ehcache

If you are using persistent disk stores, or distributed caching, care should be taken to shutdown ehcache.

Note that Hibernate automatically shuts down its ehcache CacheManager .

The recommended way to shutdown the Ehcache is:

  • to call CacheManager.shutdown()
  • in a web app, register the Ehcache ShutdownListener

    Though not recommended, ehcache also lets you register a JVM shutdown hook.

ServletContextListener

Ehcache proivdes a ServletContextListener that shutsdown CacheManager. Use this when you want to shutdown ehcache automatically when the web application is shutdown.

To receive notification events, this class must be configured in the deployment descriptor for the web application.

To do so, add the following to web.xml in your web application:

     <listener>
          <listener-class>net.sf.ehcache.constructs.web.ShutdownListener</listener-class>
     </listener>

The Shutdown Hook

Ehcache CacheManager can optionally register a shutdown hook.

To do so, set the system property net.sf.ehcache.enableShutdownHook=true .

This will shutdown the CacheManager when it detects the Virtual Machine shutting down and it is not already shut down.

When to use the shutdown hook

Use the shutdown hook where:

  • you need guaranteed orderly shutdown, when for example using persistent disk stores, or distributed caching.
  • CacheManager is not already being shutdown by a framework you are using or by your application.

    Having said that, shutdown hooks are inherently dangerous. The JVM is shutting down, so sometimes things that can never be null are. Ehcache guards against as many of these as it can, but the shutdown hook should be the last option to use.

What the shutdown hook does

The shutdown hook is on CacheManager. It simply calls the shutdown method.

The sequence of events is:

  • call dispose for each registered CacheManager event listener
  • call dispose for each Cache.

    Each Cache will:

    • shutdown the MemoryStore. The MemoryStore will flush to the DiskStore
    • shutdown the DiskStore. If the DiskStore is persistent, it will write the entries and index to disk.
    • shutdown each registered CacheEventListener
    • set the Cache status to shutdown, preventing any further operations on it.
  • set the CacheManager status to shutdown, preventing any further operations on it

When a shutdown hook will run, and when it will not

The shutdown hook runs when:

  • a program exists normally. e.g. System.exit() is called, or the last non-daemon thread exits
  • the Virtual Machine is terminated. e.g. CTRL-C. This corresponds to kill -SIGTERM pid or kill -15 pid on Unix systems.

The shutdown hook will not run when:

  • the Virtual Machine aborts
  • A SIGKILL signal is sent to the Virtual Machine process on Unix systems. e.g. kill -SIGKILL pid or kill -9 pid
  • A TerminateProcess call is sent to the process on Windows systems.

Dirty Shutdown

If ehcache is shutdown dirty then any persistent disk stores will be corrupted. They will be deleted, with a log message, on the next startup.

Replications waiting to happen to other nodes in a distributed cache will also not get written.